Geographic and Geologic Relations 



421 



butlon of the Cichlidae, the Cyprinodontidae, and the 

 southern section of the Slluridae, but with this difference 

 that none of the Characinidae were able to invade and 

 spread eastward along the Asiatic continents, (Fig 71). 

 Were we to think only of the number of existing genera and 

 species, the northern part of the S. American continent 

 would claim to be their centre of evolution. For fully 100 

 genera are S. American, while about 24 are African. Slight 

 additional proof is the finding of two fossil species of 

 Tetragonopterus in the Tertiary Lignites of San Paulo, 

 Brazil. Again, the last named genus is by far the richest 

 in living species, there being about 35 species that now ex- 

 tend from Mexico and the Guianas in the north to Buenos 

 Aires in the south. The genera also that approach it most 

 nearly in number of species, like Ciirimatiis (40), Myletes 

 and Leporinus (each 32), Prochilodiis (26), and Serras- 

 almo (23) are widely distributed over South America. 



The family has been divided by systematists into nine 

 or ten groups; of which five are purely American; two are 

 very largely so, and one of these — Hydrocyonina — is 



Fig. 71. Chart showing distribution of the Characinidae from 

 Central America or possibly northern S. America across to Africa. 

 The dark area shows distribution of the related family Gymnotidae. 



